The theory of the existence of alpha receptors in heart muscle continues to be tested at normal and low temperatures. No evidence can be found to support this theory. The effect of cardiac glycosides on skeletal muscle contraction is being investigated to determine if a positive inotropic effect exists. So far, no evidence has been found for such an effect in mammalian skeletal muscle. The effects of various agents on mast cells and lung are being studied in terms of release of histamine. Compound 48/80, antigen, ATP and various clinically used drugs, such as morphine and d-tubocurarine, release histamine. This release contributes to the shock that accompanies antigen-antibody reactions and some drug reactions.